The present invention is directed to a method for making certain hydroxy-terminated arylene ethers, such as 4,4'[arylbis(oxy)]bisphenols included within the formula, EQU HO--R--R.sup.1 --O--R--O--R.sup.1 --OH, (1)
where R is a member selected from the class consisting of C.sub.(6-30) arylene groups and C.sub.(6-30) arylene groups substituted with monovalent radicals inert during hydroxy-terminated arylene-forming reactions, R.sup.1 is a member selected from the class consisting of C.sub.(6-20) arylene radicals and C.sub.(6-30) arylene radicals substituted with monovalent radicals inert during hydroxy-terminated arylene ether-forming reactions. Preferably, the hydroxy-terminated arylene ethers of formula (1) are made by condensing an aromatic diol with 4-fluoroacetophenone followed by a Baeyer-Villiger oxidation of the resulting bisacetophenone generated to form the corresponding acetate which is thereafter hydrolyzed under basic conditions. The hydroxy-terminated arylene ethers of formula (1) are useful as flexible spacers in liquid crystalline aromatic polyesters.
Prior to the present invention, certain 4,4'[arylbis(oxy)]bisphenols included within formula (1) were prepared by the copper catalyzed Ullmann condensation of 4-methoxyphenol with a dihaloaromatic compound followed by demethylation of the resulting bismethyl ether. A less commonly used procedure for the preparation of 4,4'[arylbis(oxy)]bisphenols of formula 1 is the Ullmann condensation of 1-bromo-4-methoxybenzene with a dihydroxyaromatic compound followed by demethylation of the resulting bismethyl ether. The advantage of the second method is that readily available dihydroxyaromatic compounds can be used as starting materials.
As shown in U.S. Pat. No. 4,873,371, Yeager et al, incorporated herein by reference, hydroxy terminated arylene ethers of formula (1), were made by condensing an aromatic diol of the formula, EQU HO--R--OH, (2)
where R is as previously defined, with an arylcarbonyl compound of the formula, ##STR1## where Y is a leaving group such as fluoro, bromo or nitro and X is a member selected from the class consisting of hydrogen and a C.sub.(6-14) arylene group, to form an arylene ether dicarbonyl adduct of the formula, ##STR2## where R, R.sup.1, and X are as previously defined, thereafter oxidizing the arylene ether dicarbonyl adduct to form the corresponding arylene ether diester, ##STR3## and thereafter saponifying the arylene ether diester to form a hydroxy terminated arylene ether within formula 1.
The employment of an arylcarbonyl compound of formula (3) results in the production of the corresponding diarylphenone ethers or diarylaldehyde ethers and the corresponding aroylate or formate esters which are sometimes difficult to purify. Even though the corresponding acetates would be easier to crystallize, it was believed that the corresponding hydroxy terminated arylene ethers of formula (1), could not be readily synthesized using aromatic diol of formula (2) with an aryl alkyl ketone of the formula, ##STR4##
where Y and R.sup.1 are as previously defined, and R.sup.2 is a C.sub.(1-8) alkyl radical. The formation of the more readily crystallizable diacetate intermediates was considered less favorable, because there was potential complications in their synthesis arising from the deprotonation of the alkyl radicals adjacent to the carbonyl, leading to the formation of undesirable by-products, such as .beta.-hydroxy ketones. In addition, the intermediate arylene ether diesters of formula (5), corresponding to aroylates or formates are less readily transesterfied with carboxylic acids in the preparation of polyesters as compared to the corresponding alkyl carboxylates.
It would be desirable therefore to be able to readily synthesize arylene ether diesters by using aryl alkyl ketones of formula (6) to provide arylether diesters having R.sup.2 radicals in place of X radicals of formula (5) to produce the corresponding more readily crystallizable arylene ether bis alkyl dicarboxylates, such as the corresponding arylene ether diacetates.